Field of the Invention
Exemplary embodiments of the present invention relate to a ball-socket type tilting pad journal bearing, and more particularly, to a tilting pad journal bearing configured to reduce friction between a tilting pad and a pivot.
Description of the Related Art
Recent global research trends in super precision, an increase in speed, and a reduction in weight aim to develop a rotator system having superior reliability and high efficiency. Recently, the rotating speeds of industrial machines are gradually increased. Due to an increase in rotating speed, driving efficiency per unit volume or unit weight of rotating machines can be enhanced.
However, as the rotating speeds of the rotating machines are increased compared to before, a significant amount of vibrations are generated during an operation, thus causing problems of noise, damage to parts, and the like. Particularly, in large rotating machines such as a turbine or a generator, a heavy rotating shaft must be stably supported. For this, a bearing device is used.
In this regard, the bearing functions to fix the position of the rotating shaft and support the weight of the rotating shaft and a load applied to the rotating shaft, thus making it possible for the rotating shaft to smoothly rotate. However, a general bearing such as a rolling bearing or a sliding bearing has not only a comparatively low support stiffness but also comparatively low vibration damping performance. As a result, if a general bearing is provided for a rotating shaft of a rotating machine that rotates at high speed, there is a problem of low stability. Due to this, a tilting pad bearing is typically applied to a rotating shaft that rotates at high speed.
In particular, a tilting pad bearing that is a kind of lubrication bearing has excellent stability under conditions of high speed and is able to easily adapt to a load direction using pivots, thus exhibiting excellent bearing characteristics. Therefore, tilting pad bearings are mainly used for a high-speed/high-pressure rotating machine.
The tilting pad bearing is configured such that a plurality of tiltable bearing pads (tilting pads) are disposed around a rotating shaft in a bearing housing. Each tilting pad is tiltably supported by a pivot installed in the bearing housing. Such a bearing having tilting pads supports the rotating shaft on the tilting pads and compensates for eccentricity and tilt of the rotating shaft, thus making it possible for the rotating shaft to more reliably rotate. When the rotating shaft rotates, lubricant is guided into space between the outer circumferential surface of the rotating shaft and bearing surfaces of the tilting pads, so that a wedge-shaped oil film is formed therebetween such that the rotating shaft is reliably supported.
In the tilting pad bearing, types of supporting a pad may be classified into three types. Of them, a ball-socket type can secure structural stability under conditions of a normal load because the sizes of a ball and a socket can be appropriately selected such that the level of a pivot stress is reduced.
However, when the tilting pads are inclined at predetermined angles depending on the direction of an axial load of the rotating shaft that is rotating at high speed, friction between the tilting pads and the pivots supporting the tilting pads is caused.
Consequently, there is a problem in that lower portions of the tilting pads and the pivots are easily worn and damaged due to friction therebetween.